Tony Blair could be forced to give evidence under oath after families of 17 soldiers killed in Iraq began a legal bid yesterday to secure an independent inquiry into the lawfulness of the 2003 conflict.

A lawyer representing the families lodged papers at the high court in London, seeking a judicial review of the government's decision this May not to order an investigation into the legality of the war in Iraq.

They hope the inquiry will be held within six months.

The first three defendants named on the papers are the prime minister, the defence secretary at the time, Geoff Hoon, and the attorney general, Lord Goldsmith.

The families have demanded that judges investigate to see whether the government misled the public about the war.

Standing outside the high court, Reg Keys, the father of Corporal Tom Keys, 20, who was one of six royal military police troops killed in Majar al-Kabir, said he and the other families would not have needed to go to court had weapons of mass destruction been found in Iraq.

"We strongly feel that our sons were sent into a conflict not backed by international law or the United Nations," Mr Keys said. "Our boys were fully prepared to lay their lives down to defend their country. They were sent to war on a falsehood, against a background of propaganda of WMD. Look at the state of Iraq, it's a crucible of terror.

He added: "We feel we have to pursue this case to make our prime minister accountable for his misdemeanours. He misled parliament and it is well-known now that it was a done deal in 2002 that he was going to go to war [alongside] George Bush."

Mr Keys named 10 soldiers who lost their lives in Iraq, and the human rights lawyer Phil Shiner named families of a further seven who had signed up to the case. Mr Keys said he had travelled to the US to meet bereaved families there: "The balance has tipped and the Americans want their boys home. They are in the embryonic stages of a Vietnam."

Rose Gentle of Glasgow, whose 19-year-old, Gordon, was killed by a bomb in Basra in June 2004, said her son had been sent to Iraq "on a pack of lies". She would fight the government until she got the truth. "My campaign will continue until the troops are home."

The families argue that, under human rights laws, if the British state is involved in the use of lethal force there must be an independent inquiry.

Among the questions the families want to ask at court is why "the equivocal advice of March 7, in 2003, from the attorney general, Lord Goldsmith, changed so that 10 days later it was completely unequivocal in giving legal support for the war?"

The families are seeking an urgent preliminary hearing so the judicial review can be held before the year's end.

"Why were these soldiers sent out to Iraq when it appears from everything in the public domain that the Iraq war was illegal and that therefore the sons and daughters of these families died for no good reason?" Mr Shiner asked.

Mr Blair has said there was no need to go "back over this ground again and again". In a letter to the families, Treasury solicitors said the government believed that military action against Iraq was fully justified.